Added /upgrade endpoint (#2307)

* Added /upgrade endpoint

* fix

* Fix lints

* More lint lifex

* Move room upgrading to the roomserver

* Remove extraneous arg

* Fix HTTP API for `PerformUpgrade`

* Reduce number of API calls in `generateInitialEvents`, preserve membership fields

* Refactor `generateInitialEvents` to preserve old state events for all but the essential room setup events

* Handle ban events in the state transfer

* Refactor and comment `createTemporaryPowerLevels`

* Only send two power levels if we needed to override the levels, preserve miscellaneous fields in the create event

* Fix copyrights

* Review comments @S7evinK

* Update sytest whitelist

* Specify empty state keys, use `EventLevel`, remove unnecessary check on state copy

* Add comment to `restrictOldRoomPowerLevels`

* Ensure canonical aliases exist before clearing

* Copy invites as well as bans

* Fix return error on `m.room.tombstone` handling in client API

* Relax checks for well-formedness of join rules, membership event etc

Co-authored-by: Alex Kursell <alex@awk.run>
Co-authored-by: Neil Alexander <neilalexander@users.noreply.github.com>
Co-authored-by: kegsay <kegan@matrix.org>

roomserver/internal/api.go

@@ -34,6 +34,7 @@ type RoomserverInternalAPI struct {
 	*perform.Publisher
 	*perform.Backfiller
 	*perform.Forgetter
+	*perform.Upgrader
 	ProcessContext         *process.ProcessContext
 	DB                     storage.Database
 	Cfg                    *config.RoomServer
@@ -159,6 +160,10 @@ func (r *RoomserverInternalAPI) SetFederationAPI(fsAPI fsAPI.FederationInternalA
 	r.Forgetter = &perform.Forgetter{
 		DB: r.DB,
 	}
+	r.Upgrader = &perform.Upgrader{
+		Cfg:    r.Cfg,
+		URSAPI: r,
+	}
 
 	if err := r.Inputer.Start(); err != nil {
 		logrus.WithError(err).Panic("failed to start roomserver input API")